The belt driven data tape cartridge of Von Behren, U.S. Pat. No. 3,692,255, has become a standard interface with computers where streaming and other off-line data back-up operations require rapid acceleration and deceleration of the tape. In these tape cartridges, a belt is driven by a drive roller along a belt path which includes a portion of the peripheries of the drive roller, a supply spool, a take-up spool, and two corner guide rollers positioned adjacent the tape spools, thereby reversibly driving the tape from spool to spool. A tape path extends between the spools and along one edge of the cartridge at which access to the tape and drive roller is provided.
Belt driven tape cartridges must meet minimum tape tension specifications while simultaneously operating within maximum allowable drive force specifications. The tape tension must not fall below a certain level as the tape passes from spool to spool or contact between a read/write head and the tape will be insufficient to allow successful data transfer. The minimum tape tension should thus be as high as possible but, conversely, the maximum drive force, i.e., the force applied to rotate the cartridge drive roller, should be as low as possible so as to allow the use of an inexpensive, low-power motor in the associated drive. As these parameters are dependent on friction within the cartridge, all friction sources must be controlled. Furthermore, in the case of the corner rollers, it is desirable to maintain some non-zero level of friction between the rollers and their pivot pins.
It is known that drag in the corner roller produces a differential in belt tension which in turn produces the required tension in the tape. The latter tension is produced because tension in the portion of the belt that presses on the take-up spool, being stretched by the drive roller, causes the belt to move slightly faster and that spool to similarly rotate slightly faster than the nominal belt speed. Conversely, as the belt is basically pushed by the drive roller and hence compresses as it contacts the supply spool, the belt there moves slightly slower and thus causes that spool to rotate slightly slower. The most common method of producing such belt drag is to apply friction to the belt or to the corner rollers about which the belt extends. In the vast majority of such cartridges, and as disclosed in the aforementioned U.S. Pat. No. 3,692,255 (Von Behren), a controlled predetermined frictional coupling is provided between the corner rollers and their respective support shafts.
It has also been disclosed to utilize other techniques for restricting rotation of the corner rollers to produce controlled drag on the belt. For example, in U.S. Pat. No. 4,198,013 bowed washers are proposed to be spring-loaded on the corner roller support shafts so as to bear against the rollers to create drag. In U.S. Pat. No. 4,162,774, rubber-like, elastomeric cores are proposed to be provided within the corner rollers. These cores would then be deformed at changing regions as the roller rotates to produce a hysteresis energy loss and therefore a drag on the belt.
Most commonly, however, the drag has been provided by appropriately dimensioning and lubricating the corner roller/support shaft interface. As such lubricants may change in viscosity over the life of the cartridge or may migrate from the interface, oil-retaining structures have been proposed (Jap. Kokai No. 63-114471). An oriented, controlled texture including axial splines is disclosed in German Patent Appln. No. G-9101648.7.